1. Field
The present invention relates generally to techniques for performing wellsite operations. More specifically, the present invention relates to techniques, such as a tubular centering device and/or a blowout preventer (BOP).
2. Description of Related Art
Oilfield operations are typically performed to locate and gather valuable downhole fluids. Oil rigs may be positioned at wellsites and downhole tools, such as drilling tools, may be deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubulars or tubular strings may be positioned in the wellbore to enable the passage of subsurface fluids from the reservoir to the surface.
Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. Equipment, such as BOPs, may be positioned about the wellbore to form a seal about a tubular therein, for example, to prevent leakage of fluid as it is brought to the surface. BOPs may have selectively actuatable rams or ram bonnets, such as tubular rams (to contact, engage, and/or encompass tubulars to seal the wellbore) or shear rams (to contact and physically shear a tubular), that may be activated to sever and/or seal a tubular in a wellbore. Some examples of ram BOPs and/or ram blocks are provided in U.S. Pat. Nos. 3,554,278; 4,647,002; 5,025,708; 7,051,989; 5,575,452; 6,374,925; 7,798,466; 5,735,502; 5,897,094 and 2009/0056132. Techniques have also been provided for cutting tubing in a BOP as disclosed, for example, in U.S. Pat. Nos. 3,946,806; 4,043,389; 4,313,496; 4,132,267; 2,752,119; 3,272,222; 3,744,749; 4,523,639; 5,056,418; 5,918,851; 5,360,061; 4,923,005; 4,537,250; 5,515,916; 6,173,770; 3,863,667; 6,158,505; 4,057,887; 5,505,426; 3,955,622; 7,234,530 and 5,013,005. Some BOPs may be provided guides as described, for example, in U.S. Pat. Nos. 5,400,857, 7,243,713 and 7,464,765.
Despite the development of techniques for cutting tubulars, there remains a need to provide advanced techniques for more effectively sealing and/or severing tubulars. The present invention is directed to fulfilling this need in the art.